Cartridges for use in firearms are well known. Such cartridges typically comprise a shell, which contains gun powder, and a bullet. The shell comprises a cylindrical casing with a closed end at its base and an open end opposite the base of the shell. If the base extends radially out beyond the casing, the cartridge is termed a "rim fire cartridge." The bullet is secured to the open end of the shell at the end opposite from the base. Magazines for holding cartridges are well known in the art. The magazine can be designed to contain anywhere from a few cartridges to as many as 50 or more cartridges. When the firearm is to be used, the magazine is inserted and secured in the "well" of the firearm. The magazine can be easily detached from the firearm, for instance, to reload the magazine or while the firearm is being stored or transported. The well of a firearm typically has linear, parallel side walls. Therefore, the portion of the magazine which is to be received into the well must also have corresponding linear, parallel exterior walls in order to fit securely within the well. Typically the well also has a latch means which engages corresponding latch engaging means on the magazine so that the magazine can be locked securely in the well.
A problem arises when a large number of rim fire cartridges are stacked in a magazine. Because the diameter of the rim is larger than the diameter of the rest of the cartridge, the cartridges do not line up in a parallel manner when stacked in a magazine. One solution to this problem has been to design magazines that only hold a small number of cartridges (e.g. about seven). In this way, even though the cartridges are not parallel, the total deviation is not too great. However, when it is desired to hold a larger number of cartridges, the variation in cartridge diameter becomes a more pronounced problem. This is because the variation is additive, i.e., when each additional cartridge is stacked in the magazine, the difference in diameter due to the rim forces the adjacent cartridge out of alignment by an additional incremental amount equal to the difference in diameter between the rim and the rest of the cartridge.
This problem has been alleviated by the use of arcuate shaped magazines. The rim of the cartridge is accommodated near the end wall of the magazine which comprises the larger arc segment and the bullet nose points toward the end wall having the shorter arc segment. A typical arcuate shaped cartridge magazine is illustrated in U.S. Pat. No. 4,127,954 to Hausmann. But the use of an arcuate shaped magazine raises another problem because the firearm well is typically not arcuate shaped, but rather linearly shaped. Therefore, the head of the Hausmann magazine which fits into the firearm well is linearly shaped. Because of this modification of the outer surface, it was also necessary to modify the inner configuration of the magazine. In the Hausmann patent, the inner surface of the magazine head has two opposed linearly-extending inner surfaces adjacent to the bullet nose and rim of each cartridge. This necessity of modifying the inner configuration has resulted in many troubles such as the jamming of a cartridge in its translation of movement from an arcuate direction to a linear direction.
In U.S. Pat. No. 4,566,212, to Chesnut, who is also the inventor of the present invention, a cartridge magazine is provided wherein the rim of each cartridge is guided by means so that each cartridge has a continuous arcuate movement throughout the entire extent of the magazine. The magazine has an outer surface which is generally arcuately shaped at one end thereof (which will be termed the magazine "body") and also has an outer surface that is generally linearly shaped at the end that is inserted into the firearm well (which will be termed the magazine "head"). The inner surfaces of the magazine are arcuately shaped and extend throughout the extent of the magazine. Portions of the rim of each cartridge are located in the grooves so that each cartridge moves in an arcuate direction throughout the magazine. This magazine solves the problem of fitting an arcuate shaped magazine into a well with parallel linear walls while at the same time providing continuous arcuate movement throughout the magazine for the cartridge.
However, when it is desired to construct magazines such as those disclosed in U.S. Pat. No. 4,566,212 out of a plastic material, provisions must be made for joining parts of the magazine together. Presently the magazine is made in two separate halves by injection molding. The two separate halves are then joined together by ultrasonic welding. This method of manufacture has worked satisfactorily for magazines designed for various models of firearms. It has recently been discovered, however, that magazines manufactured in this way cannot be accommodated in some firearm wells. The problem is due to the fact that the wells are designed such that the physical dimension difference between the firearm well and the cartridges is slight. In other words, the size of the well is not much larger than the size of the cartridge. The effect of such a small physical dimension difference is that the wall of the magazine head must be quite thin in order to accommodate the cartridge inside the head while still being able to fit within the well. In the past, the solution to this problem has been to design magazines in which both the interior and exterior configuration are linear. In addition, prior art magazines for wells having this slight dimensional difference are typically constructed out of metal, which, because of a higher strength per unit volume ratio than most plastics, allows for thin walls without the loss of structural integrity.
The problem identified by the present invention was how to design and construct a magazine which has an arcuate shaped interior and a head with a linearly shaped exterior, while still being able to fit the head into a well having a very small dimensional difference between the well and the cartridge. Because the arcuate shaped interior does not efficiently fit within the space provided by a linearly shaped exterior, the thickness of the end walls must vary. The thickness of the end walls not only affects the structural integrity of the magazine, but it also affects the method of manufacturing. If the magazine is made of plastic by the prior art method of welding two halves together, the end walls must be greater than a certain minimum thickness in order that the corresponding mating surfaces of the halves are wide enough to weld together. However, this minimum thickness is not available in the end walls of a head designed to fit in a well having only a slight size difference.
Therefore, it would be advantageous to have a magazine with an arcuately shaped interior and having a head portion which has a linearly shaped exterior which is able to fit within a linearly shaped firearm well having a slight dimensional difference between the well and the cartridge. It would also be advantageous to construct such a magazine from plastic and yet maintain the structural integrity of the magazine.